Process for preparing aluminum salts of organic phosphoric acids

ABSTRACT

The invention concerns a process for preparing salts of organic acids of phosphorus. The organic acid is reacted with aluminum hydroxide in the presence of a polar solvent selected from acetic acid, propionic acid, methanol, ethanol, n-propanol, isopropanol, butanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, and acetonitrile.

The invention relates to a process for the preparation of aluminum saltsof organic acids of phosphorus. More specifically, these are phosphonichalf-esters, phosphinic acids and phosphonous acids.

The aluminum salts of these organic phosphoric acids are valuable flameretardants.

Aluminum salts of phosphonic half-esters have hitherto been prepared byreacting aluminum chloride with phosphonic diesters (EP-A 245 207), byreacting elemental aluminum with phosphonic diesters (EP-A 299 922) andby reacting aluminum hydroxide with phosphonic diesters in the absenceof water at 180° C. (EP-A 327 496). Aluminum salts of phosphinic acidsand cyclic phosphinic acids (1-hydroxy-dihydrophosphole oxides and1-hydroxy-phospholane oxides) have hitherto been prepared by reactionwith aluminum hydroxide in water (EP-A2-0 699 708).

The reaction of phosphonic diesters with aluminum chloride, aluminum oraluminum hydroxide inevitably leads to undesired byproducts such asalkyl chlorides, alcohols, carbon monoxide, ethylene, ethane and lowdialkyl ethers. The phosphonic diesters also have to be used in excess.The reaction of organic phosphoric acids in water with aluminumhydroxide is in itself technically simple. A disadvantage is the longreaction time which is required.

There was therefore a need to develop a process which avoids theaforementioned disadvantages, is industrially feasible without greatexpenditure and, moreover, makes the desired products available both inhigh yield and in high purity.

Surprisingly, this object was achieved by a process for the preparationof aluminum salts of organic phosphoric acids of the formula (I)

where

R¹ is a saturated or unsaturated or unbranched C₁-C₈, preferably C₁-C₄alkyl, or phenyl,

when n=0

R² is as defined for R¹ or is hydrogen, it also being possible for R¹and R² to be joined to give a saturated or unsaturated ring,

when n=1

R² is a saturated C₁-C₄ preferably C₁, alkyl, which comprises reacting,in the absence or presence of water, organic phosphoric acids of theformula (II)

where R¹, R² and n are as defined above, with aluminum hydroxide in thepresence of polar solvents.

Surprisingly, it was found that the chemically largely inert aluminumhydroxide reacts more quickly in the presence of polar solvents.

Examples of organic phosphoric acids which may be mentioned are:

1. Phosphonic monoesters: monomethyl methanephosphonates, monomethylpropanephosphonates, monoethyl ethanephosphonates, mono-n-propylphenylphosphonates.

2. Phosphinic acids: dimethylphosphinic acid, ethylmethylphosphinicacid, propylmethylphosphinic acid, methylphenylphosphinic acid.

3. Cyclic phosphinic acids: 1-hydroxy-3-methyl-2,5-dihydro-1H-phosphole1-oxide, 1-hydroxy-2,3-dihydro-1H-phosphole 1-oxide,1-hydroxy-2,5-dihydro-1H-phosphole 1-oxide, 1-hydroxy-1H-phospholane1-oxide and 1-hydroxy-3-methyl-1H-phospholane 1-oxide.

4. Phosphonous acids: methanephosphonous acid, propanephosphonous acid,octanephosphonous acid, phenylphosphonous acid.

Polar solvents which may be mentioned in particular are: acetic acid,propionic acid, methanol, ethanol, propanol, butanol, acetone, methylethyl ketone, tetrahydrofuran, dioxane and acetonitrile. Acetic acid andisopropanol are particularly preferred.

The solvents can also be used as mixtures. In particular, mixtures withwater can be used advantageously.

The reaction temperatures are 50 to 200° C., preferably 70 to 100° C.The reaction is preferably carried out under reflux conditions. Athigher temperatures, the reaction may be carried out under pressure.

The reaction components can be mixed with the solvents and are thenusually stirred for several hours at the desired reaction temperature.It can also be advantageous to introduce the solvent or solvent mixturewith aluminum hydroxide, and slowly meter in the organic phosphoric acidat the reaction temperature with continuous stirring. After the reactionhas finished, the mixture is filtered off with suction and the aluminumsalt produced is dried. In the process of the present invention, thealuminum salts which are produced are finely particulate with a meanparticle size of from 2 to 25 μm. It is not therefore necessary to grindthese salts after drying for plastics compounding.

EXAMPLE 1 Aluminum Salt of Monomethyl Methanephosphonate

99 g (0.9 mol) of monomethyl methanephosphonate, 23.4 g (0.3 mol) ofaluminum hydroxide and 330 ml of water/solvent mixture are stirred atthe reaction temperature for the reaction period. Filtration withsuction is then carried out, followed by washing with water/solventmixture and drying at 140-150° C. in a vacuum drying cabinet to give thereaction product.

Reaction Reaction temperature period Yield % of No. Water/solventmixture [° C.] [h] [g] theory a Water/isopropanol 75 24 96.7 91 1:1 bWater/isopropanol 75 12 97.5 92 1:1 c Water/acetic acid 80-90 24 92.987.5 1:1

EXAMPLE 2 Aluminum Salt of Ethylmethylphosphinic Acid with Acetic Acidor Propionic Acid as Solvent

54 g (0.5 mol) of ethylmethylphosphinic acid, 13 g (0.167 mol) ofaluminum hydroxide and 154 ml of solvent or solvent mixture are stirredat the reaction temperature for the reaction period. Cooling andfiltration with suction are then carried out, followed by drying at140-150° C. in a vacuum drying cabinet to give the reaction product.

Reaction Reaction temperature period Yield % of No. Water/solventmixture [° C.] [h] [g] theory a Acetic acid 105 4.5 54 93 b Aceticacid/water 86 5 50.1 86 2:1 c Propionic acid 115-120 5 52.2 90

EXAMPLE 3 Aluminum Salt of Ethylmethylphosphinic Acid with Other PolarSolvents

108 g (1.0 mol) of ethylmethylphosphinic acid, 26 g (0.333 mol) ofaluminum hydroxide and 324 ml of solvent or solvent mixture are stirredat the reaction temperature for the reaction period. Cooling, filtrationwith suction and drying are then carried out.

Reaction Reaction temperature period Yield % of No. Water/solventmixture [° C.] [h] [g] theory a Isopropanol 85 24 92.5 80 bIsopropanol/water 85 7.5 110.9 96 1:1 c Methanol/water 80 24 100.8 88

EXAMPLE 4 Aluminum Salt of Ethylmethylphosphinic Acid

130 g (1.67 mol) of aluminum hydroxide and 1620 ml of acetic acid areheated to reflux with stirring, and 540 g (5.0 mol) ofethylmethylphosphinic acid are added dropwise over the course of 3.5hours. The mixture is then maintained under reflux for about another 4hours. Filtration with suction is carried out, followed by drying in avacuum drying cabinet at 140° C., giving 573 g. This corresponds to ayield of 98.6% of theory.

EXAMPLE 5 Aluminum Salt of Methylpropylphosphinic Acid

91.5 g (0.75 mol) of methylpropylphosphinic acid are dissolved in 240 mlof acetic acid, and 19.5 g (0.25 mol) of aluminum hydroxide are added.The mixture is then heated at 110° C. with stirring for 5 hours, cooledand filtered with suction. Drying in a vacuum drying cabinet at 140° C.gives 85 g. This corresponds to a yield of 87% of theory.

EXAMPLE 6 Aluminum Salt of 1-hydroxy-1H-phospholane 1-oxide

10 g (0.083 mol) of 1-hydroxy-1H-phospholane 1-oxide and 2.2 g (0.028mol) of aluminum hydroxide are stirred into 28 ml of acetic acid at 105°C. for 1.5 hours. The mixture is then filtered with suction, giving 10.5g which after drying do not melt up to 360° C. This corresponds to ayield of 98% of theory.

EXAMPLE 7 Aluminum Salt of 1-hydroxy-3-methyl-1H-phospholane 1-oxide

26.8 g (0.200 mol) of 1-hydroxy-3-methyl-1 H-phospholane 1-oxide and 5.2g (0.067 mol) of aluminum hydroxide are stirred into 33 g of acetic acidat 105° C. for 4 hours. The mixture is then filtered with suction,giving 26.2 g which after drying do not melt up to 360° C. Thiscorresponds to a yield of 92% of theory.

EXAMPLE 8 Aluminum Salt of 1-hydroxy-2,5-dihydro-1H-phosphole 1-oxide

10 g (0.085 mol) of 1-hydroxy-2,5-dihydro-1H-phosphole 1-oxide and 2.2 g(0.028 mol) of aluminum hydroxide are stirred into 28 ml of acetic acidat 105° C. for 1.5 hours. The mixture is then filtered with suction,giving 10.5 g which after drying do not melt up to 360° C. Thiscorresponds to a yield of 97% of theory.

EXAMPLE 9 Aluminum Salt of Methanephosphonous Acid

80 g (1.0 mol) of methanephosphonous acid are dissolved in 110 ml ofacetic acid, and 26 g (0.33 mol) of aluminum hydroxide are added withstirring. The mixture is then heated at 110° C. for 5 hours. Cooling,filtration with suction and drying at 140° C. in a vacuum drying cabinetgive 82.7 g, which corresponds to a yield of 94% of theory.

What is claimed is:
 1. A process for the preparation of an aluminum saltof an organic acid of phosphorus, which comprises reacting the organicacid of phosphorus with a aluminum hydroxide in a polar solvent, andwherein the organic acid of phosphorus is selected from the groupconsisting of phosphonic monoester, phosphinic acid, cyclic phosphinicacid and phosphonous acid and wherein the polar solvent is selected fromthe group consisting of acetic acid, propionic acid, methanol, ethanol,n-propanol, isopropanol, butanol, acetone, methyl ethyl ketone,tetrahydrofuran, dioxane and acetonitrile.
 2. The process of claim 1,wherein the organic acid of phosphorus is reacted with aluminumhydroxide in the presence of water.
 3. The process of claim 1, whereinthe process is carried out at a reaction temperature in the range from50° C. to 200° C.
 4. The process of claim 1, wherein a salt of anorganic acid of phosphorus with a mean particle size of from 2 to 25 μmis formed in the process.